In the present state of the art closure systems with a plurality of locks require a coordination center which stores all valid codes of all locks so that they can be called up selectively, which exchanges varied codes and which executes all coordination work which occurs. Passive keys, e.g. in the form of puched cards, are used advantageously. They are coded in the center. The center must consequently communicate or be in contact with the individual locks, which normally requires expensive installations between the coordination center and the various locks which are susceptible to intervention by force. While searching for remedies, methods have been found which omit the above-mentioned installations by executing the necessary exchange of data between the center and the locks by way of the keys which are employed. Such a method is disclosed in U.S. Pat. No. 3,800,284. It permits the respective valid code to be varied through the coordination center at arbitrarily chosen times. If such an alteration is to be performed, the coordination center produces a newly coded key for the respective lock. The key code has been derived from the hitherto valid key code with the aid of a pseudo random generator. If the actuated lock logic circuit now recognizes that the key code being offered corresponds to the hitherto valid lock code which has been modified in the same way on the lock side, it accepts this and assumes it to be the new lock code, thus enabling this key to still fit the lock, while the hitherto proper key has been blocked or eliminated due to the change in the lock code.
Another similar method is recited in U.S. Pat. No. Re 29,259 which has the same object and accomplishes this in a similar manner. The essential difference is that in this case the key contains two different codes, an authorization code and a key code. According to which of the two codes present on the key side coincides with the respective lock code, the lock is only opened or it also uses the offered authorization code as the future valid lock code. In this case as well, the appropriate coding of a key determines whether or not the lock code is to be altered to block the hitherto proper key. The advantages over the first above-mentioned process are quite obvious: true random codes can be used for recoding and the lock logic circuit does not require a pseudo random generator. In both methods the use of additional keys is provided, each of them fitting a plurality of locks (e.g. personnel keys in hotels). In such expanded systems, keys and/or locks possess additional codes which must be evaluated in the same manner.
Compared to the instant invention, the above methods demonstrate the following essential differences. A relatively expensive stationary coordination central is required for the coordination work. The center can be misused, since it is not safeguarded. It requires all valid lock codes. Disruptions or malfunctions, e.g. due to memory break-down or erroneous codes on the lock side, cannot be corrected at all in the one system and only with difficulty in the other one. The codes cannot be changed automatically every time the key is used. Keys which have access to a plurality of locks have the same codes for these locks. This means a restriction of the safety of the system and a problematical change of key/lock associations.
A second group of methods does not necessitate any coordination center. They advantageously employ active electronic keys which have their own reprogrammable memories, e.g. IC shift registers or core memories, to receive and intermediately store variable codes. Such methods make it possible to change the valid lock/key code at any time during a key contact with a lock so that it is possible to automatically alter the valid codes every time the lock is actuated. Such measures enhance the safety of the system considerably. What is problematical, however, is the coordination of a plurality of such keys for a common lock or the execution of other tasks which are relatively easy to solve with the aid of a center such as, for example, the replacement of lost or stolen proper keys, the elimination of erroneous codes, the change of key/lock associations etc. A method of the second group is dislcosed in the associated U.S. Pat. No. 3,848,229 and 3,859,634. Of the aforequoted problems associated with this group of methods, only one is solved at the expense of free code changes: the coordination of a plurality of keys for a common lock. Individual code sites are combined according to an established scheme from a binary code present on the lock side (partial codes) and respectively associated with a key. The number of partial codes of a lock determines the number of auxiliary or additional keys employed. Identical partial codes of different locks can be actuated by the same key. The consequence is that the safety of the system is restricted, the codes can no longer to chosen arbitrarily, and automatic code changes cannot be realized according to a random or pseudo random law. The safety measures given for this method and designed to prevent valid key codes from being read out and to serve automatic user identification are easy to circumvent unlike the corresponding measures in the instant invention.
Another method in the second group, which incidentally operates only with pseudo random combinations, is disclosed in U.S. Pat. No. 3,944,976. Of the problems of this method group mentioned at the outset, this method only solves the coordination of a plurality of keys for one common lock (or vice-versa) this time at the expense of operational comfort, since the lock/key association must be executed manually on the key before the key is used. The key/lock association produced in this manner ensures that of a plurality of codes stored on the lock side only the one code chosen by the association will be processed. The coincidence examination is made for all codes. If one of them coincides with the offered key code, this is sufficient to release the lock. The consequence is that operation is cumbersome, errors in operation can also block other keys, every lock requires a differently constructed key receptacle and, since there is no selective code examination, the safety of the system is restricted.
Methods of the second group have the following essential differences as compared to the instant invention. The use of a plurality of keys for one common lock (or vice-versa) is conductive to a restriction of the safety of the system and, in addition, to the omission of arbitrarily selectable or automatically changing codes or operational difficulties in addition to a possible impairment of other users. The lock/key associations cannot be varied without intervention. An undesirable blocking of an originally proper key, for instance due to a contact interruption during data exchange, cannot be eliminated or corrected without intervention. If a proper key is lost, a proper replacement cannot be manufactured by the user. Interventions in the respective lock circuits are required to block the lost key. The system can be tricked by overloading the active memory arrays of the lock and keys, e.g. by overheating, so that they are energized in technologically-induced preferential positions (smoothed codes) which trigger release by virtue of the code coincidence achieved in this way.
Finally, other differences are mentioned which both method groups include as compared to the instant invention. New lock and key codes are not corrected if the codes are erroneous. The undesirable duplication of a key is not prevented at all or only poorly. User identification does not exist or it can be faked. If the system malfunctions, e.g. if the lock memory is erased, the safety of the system works against the user.